Complementary acceptor and site specificities of Fuc-TIV and Fuc-TVII allow effective biosynthesis of sialyl-TriLex and related polylactosamines present on glycoprotein counterreceptors of selectins.
The P-selectin counterreceptor PSGL-1 is covalently modified by mono alpha2,3-sialylated, multiply alpha1,3-fucosylated polylactosamines. These glycans are required for the adhesive interactions that allow this adhesion receptor-counterreceptor pair to facilitate leukocyte extravasation. To begin to understand the biosynthesis of these glycans, we have characterized the acceptor and site specificities of the two granulocyte alpha1,3-fucosyltransferases, Fuc-TIV and Fuc-TVII, using recombinant forms of these two enzymes and a panel of synthetic polylactosamine-based acceptors. We find that Fuc-TIV can transfer fucose effectively to all N-acetyllactosamine (LN) units in neutral polylactosamines, and to the "inner" LN units of alpha2,3-sialylated acceptors but is ineffective in transfer to the distal alpha2,3-sialylated LN unit in alpha2,3-sialylated acceptors. Fuc-TVII, by contrast, effectively fucosylates only the distal alpha2,3-sialylated LN unit in alpha2,3-sialylated acceptors and thus exhibits an acceptor site-specificity that is complementary to Fuc-TIV. Furthermore, the consecutive action of Fuc-TIV and Fuc-TVII, in vitro, can convert the long chain sialoglycan SAalpha2-3'LNbeta1-3'LNbeta1-3'LN (where SA is sialic acid) into the trifucosylated molecule SAalpha2-3'Lexbeta1-3'Lexbeta1-3'Lex (where Lex is the trisaccharide Galbeta1-4(Fucalpha1-3)GlcNAc) known to decorate PSGL-1. The complementary in vitro acceptor site-specificities of Fuc-TIV and Fuc-TVII imply that these enzymes cooperate in vivo in the biosynthesis of monosialylated, multifucosylated polylactosamine components of selectin counterreceptors on human leukocytes.
Niemelä
R
R
Institute of Biotechnology, P.O. Box 56, University of Helsinki, FIN-00014 Helsinki, Finland.
Natunen
J
J
Majuri
M L
ML
Maaheimo
H
H
Helin
J
J
Lowe
J B
JB
Renkonen
O
O
Renkonen
R
R
D000606:Amino Sugars / Q000096:biosynthesis* / Q000737:chemistry / Q000378:metabolism; D000818:Animals; D016466:CHO Cells; D002240:Carbohydrate Sequence; D006224:Cricetinae; D005643:Fucose / Q000378:metabolism; D005647:Fucosyltransferases / Q000378:metabolism*; D006098:Granulocytes / Q000201:enzymology; D006801:Humans; D008562:Membrane Glycoproteins / Q000378:metabolism*; D008969:Molecular Sequence Data; D009844:Oligosaccharides / Q000737:chemistry / Q000378:metabolism; D011134:Polysaccharides / Q000096:biosynthesis* / Q000737:chemistry / Q000378:metabolism; D011994:Recombinant Proteins / Q000378:metabolism; D019087:Selectins / Q000502:physiology; D013379:Substrate Specificity
D000606:Amino Sugars; D008562:Membrane Glycoproteins; D009844:Oligosaccharides; C084882:P-selectin ligand protein; D011134:Polysaccharides; D011994:Recombinant Proteins; D019087:Selectins; C066929:polylactosamine; D005643:Fucose; C000458:N-acetyllactosamine; D005647:Fucosyltransferases; C031692:galactoside 3-fucosyltransferase